This invention relates to wafer carriers. More particularly it relates to composite wafer carriers for the storage and handling of very thin semiconductor wafer disks.
The processing of wafer disks into integrated circuit chips often involves several steps where the disks are repeatedly processed, stored and transported. Due to the delicate nature of the disks and their extreme value, it is vital that they are properly protected throughout this procedure. One purpose of a wafer carrier is to provide this protection. Additionally, since the processing of wafer disks is generally automated, it is necessary for disks to be precisely positioned relative to the processing equipment for the robotic removal and insertion of the wafers. A second purpose of a wafer carrier is to securely hold the wafer disks during transport.
The conventional wafer carrier is a single molded part generally comprising a front end having an H-bar interface portion, a back end having a panel, and sidewalls having slots and lower curved or converging portions following the curvature of the wafers, and with an open top and open bottom. Conventional carriers generally have standardized dimensions so as to be relatively interchangeable and useable with robotic processing equipment from a variety of manufacturers. For example, the xe2x80x9cpitchxe2x80x9d, or distance between the same surface of wafers stored in adjacent slots, is typically 0.250 inch, while the depth of the slot at each sidewall is typically 0.750 inch.
Recently, the semiconductor industry has begun using wafer disks having a very thin cross sectional dimension. The thickness of these wafers can be less than 0.1 mm, in contrast with a typical conventional wafer thickness of 0.75 mm. These thin wafers present unique design considerations, and conventional carriers are unsatisfactory in several respects for use with them.
When supported at the periphery of the wafer and oriented with the planar surface of the wafer parallel to the ground, the thin wafer tends to sag to a much greater degree than a conventional wafer. If the amount of sag is excessive, access to the individual wafers with automatic processing equipment is inhibited. In some cases, adjacent wafers can even contact each other, causing damage to the wafers.
Another characteristic of thin wafers is that they can be even more brittle and prone to physical damage than a standard wafer. A conventional wafer carrier, having support for the wafer only proximate to the extreme periphery of the wafer, causes beam loading to be imposed on the wafer by its own dead weight. The stress imposed by this beam loading makes the wafer even more prone to physical damage from shock or vibration.
The edges of thin wafers can be very sharp, not only because they are formed from very hard materials, like silcon, but also because of the high unit pressures that can be exerted at the thin edges. Consequently, thin wafers may cut through softer materials that come into contact with the peripheral edge of the water, for example the wafer carrier plastic.
Finally, there has been little if any standardization of wafer thickness in thin wafers. Conventional wafer carriers having a fixed pitch dimension are insufficiently flexible to handle a wide range of wafer thicknesses and consequent deflections.
There is a need for a wafer carrier specifically designed so as to be suitable for use with very thin wafers.
The present invention is a wafer carrier specially suited for thin wafers. The carrier of the present invention has a number of distinct advantages as compared with conventional carriers, especially for use with very thin wafers. A larger pitch dimension between adjacent wafers allows more clearance between wafers to prevent wafer-to-wafer contact, increased clearance for automated wafer handling tools, and increased clearance to prevent contact with adjacent shelves at the wafer edges. Upwardly canted shelves create contact only along a narrow line at the furthest inside edge of the shelf, thus minimizing the contact area between the wafer and shelf, providing continuous support for the wafer along a large portion of its circumference, and moving the area of support as far toward the center of the wafer as possible to minimize beam loading and sagging of the wafer. Also, the increased shelf depth dimension moves the wafer support area closer to the center of the wafer for the same purpose. The above shelf features may be used together in a single carrier or may be selected in any combination, as allowed by the flexible configuration of the. sidewall assemblies and other portions of the carrier, in order to achieve a carrier having optimal features for carrying any particular thin wafer configuration. Sidewall assemblies comprised of individual shelf members may be removably interlocked together allow the carrier to be quickly and easily reconfigured with slots of different pitch dimensions, shelf depth dimensions, and shelf angles so as to accommodate wafers of different thickness and dimension as described above.
The invention may accordingly be characterized in a currently most preferred embodiment as a wafer carrier for carrying a plurality of axially aligned thin circular wafers. The carrier has a framework portion formed by a pair of end members connected by a plurality of side support members. A pair of opposing sidewall assemblies is positioned between the pair of end members and is attached to at least one of the plurality of side support members. Each sidewall assembly has a plurality of shelves defining a plurality of slots for receiving a wafer, and comprises a plurality of stacked together individual shelf members. Each shelf member has a body portion with an upper surface and a lower surface. The lower surface has a plurality of projecting pegs, and the upper surface has a plurality of apertures for receiving the plurality of pegs of an immediately adjacent individual shelf member.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.